如何并行化文件下载？

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如何解决如何并行化文件下载？？

您可以使用线程池并行下载文件：

#!/usr/bin/env python3
from multiprocessing.dummy import Pool # use threads for I/O bound tasks
from urllib.request import urlretrIEve

urls = [...]
result = Pool(4).map(urlretrIEve, urls) # download 4 files at a time

您还可以使用asyncio以下命令在一个线程中一次下载多个文件：

#!/usr/bin/env python3
import asyncio
import logging
from contextlib import closing
import aiohttp # $ pip install aiohttp

@asyncio.coroutIne
def download(url, session, semaphore, chunk_size=1<<15):
    with (yIEld from semaphorE): # limit number of concurrent downloads
        filename = url2filename(url)
        logging.info('downloading %s', fileName)
        response = yIEld from session.get(url)
        with closing(responsE), open(filename, 'wb') as file:
            while True: # save file
                chunk = yIEld from response.content.read(chunk_sizE)
                if not chunk:
                    break
                file.write(chunk)
        logging.info('done %s', fileName)
    return filename, (response.status, tuple(response.headers.items()))

urls = [...]
logging.basicConfig(level=logging.INFO, format='%(asctimE)s %(messagE)s')
with closing(asyncio.get_event_loop()) as loop, \
     closing(aiohttp.ClIEntSession()) as session:
    semaphore = asyncio.Semaphore(4)
    download_tasks = (download(url, session, semaphorE) for url in urls)
    result = loop.run_until_complete(asyncio.gather(*download_tasks))

这里url2filename()定义在哪里。

解决方法

import urllib.request

urls = ['foo.com/bar.gz','foobar.com/barfoo.gz','bar.com/foo.gz']

for u in urls:
  urllib.request.urlretrieve(u)

import subprocess
import os

def parallelized_commandline(command,files,max_processes=2):
    processes = set()
    for name in files:
        processes.add(subprocess.Popen([command,name]))
        if len(processes) >= max_processes:
            os.wait()
            processes.difference_update(
                [p for p in processes if p.poll() is not None])

    #check if all the child processes were closed
    for p in processes:
        if p.poll() is None:
            p.wait()

urls = ['http://www.statmt.org/wmt15/Training-monolingual-nc-v10/news-commentary-v10.en.gz','http://www.statmt.org/wmt15/Training-monolingual-nc-v10/news-commentary-v10.cs.gz','http://www.statmt.org/wmt15/Training-monolingual-nc-v10/news-commentary-v10.de.gz']

parallelized_commandline('wget',urls)

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